The invention relates to a device for slag-free pouring into a continuous casting machine with a slide gate nozzle at the discharge orifice of a tundish and a starting pipe blocking the inlet of the discharge orifice when filling the tundish.
Such devices have as a goal to allow only clean or pure molten metal at as high as possible a temperature or without significant heat loss through cooling into the discharge opening of the tundish and thus through the slide gate nozzle into a mold of the continuous casting machine.
A refractory starting pipe with an ideal break point having the shape of an annular slot and breaking under the burn-through effect and/or the buoyancy of the molten metal is disclosed in DE-OS 3 701 707. The broken off piece of pipe floats and thus clears the way for the melt to the discharge orifice of the vessel via the remainder of the pipe that remains in position at the bottom of the vessel. Thus, the opening procedure is a function of the functional efficacy of the ideal break point at a desired instant. If the ideal break point does not break in time, the break must be produced by manipulating a rod from the outside, a process that is irksome and, especially in the case of multistrand machines, time-consuming and expensive. On the other hand, the ideal break point can function earlier than intended so that slag floating on the molten metal is carried along into the discharge orifice and deposited into the mold via a dummy bar head thereof. Such non-metallic nests in the mold always mean a risk associated with the breakthrough of the melt when the dummy bar starts to withdraw.
Therefore, in the practice one usually drops the application of covering flux for thermal insulation and air shielding of the melt directly after generation of a melt level in the tundish. This does not occur until after the release of the molten metal flow by means of the starting pipe so that a significant heat loss and reoxidation of the melt must be taken into account, a state that can be the cause of melt deposits or freezings forming by themselves in the slide gate nozzle.